Recycled Superabsorbent Polymer Particles

ABSTRACT

The present invention relates to absorbent cores comprising recycled superabsorbent polymer particles which have previously been immobilized by a solidified thermoplastic composition. The superabsorbent polymer particles can be separated from the solidified thermoplastic composition by using a supercritical fluid such as carbon dioxide, propane or mixtures thereof.

FIELD OF THE INVENTION

The present invention relates to recycling of superabsorbent polymerparticles which have previously been immobilized by a solidifiedthermoplastic composition. The superabsorbent polymer particles can beseparated from the solidified thermoplastic composition by using asupercritical fluid comprising carbon dioxide, propane or mixturesthereof.

BACKGROUND OF THE INVENTION

In the course of high speed manufacturing disposable absorbent articles,such as diapers and sanitary napkins, it is common to detect defect orimperfect articles and discard them from the production process. Thoughnot suitable for sale, these waste products may contain materials, whichare too valuable to be thrown away. Instead, it may be desirable toretrieve certain materials from the defect product. Especially, it isdesirable to regain the superabsorbent polymer particles typicallycomprised in disposable absorbent articles.

Today, most disposable diapers use absorbent cores with superabsorbentpolymer particles intermingled with pulp fibers (so-called “airfelt”),such as cellulose fibers. In these diapers, the superabsorbent polymerparticles are largely held in place by the surrounding pulp fibers. Thesuperabsorbent polymer particles may therefore be retrieved by shreddingthe articles and shaking the superabsorbent polymer particles out e.g.via vibration, freeing the particles from the surrounding pulp fibers.

However, moving to absorbent articles wherein the absorbent cores arefree from airfelt or wherein the absorbent cores contain only smallamounts of airfelt, the superabsorbent polymer particles have to beimmobilized by different means, as they can no longer be held in placeby surrounding pulp fibers. One way to immobilize the superabsorbentpolymer particles within the absorbent core is by using adhesives. Theseadhesives, though used in small amounts relative to the amount ofsuperabsorbent polymer particles, closely adhere to the superabsorbentpolymer particles. Apart from attaching the superabsorbent polymerparticles to each other, the adhesives can also affix the superabsorbentpolymer particles to a carrier substrate, such as a nonwoven web.Thereby, the particles cannot simply be shaken out to recycle them.

It would be desirable to have a method for separating superabsorbentpolymer particles from the adhesives in order to regain the particles.It would further be desirable to be able to recycle the superabsorbentpolymer particles after separation by introducing them in other, newlymanufactured absorbent articles. Therefore, the performance of thesuperabsorbent polymer particles, particularly regarding theirpermeability, but also with respect to their capacity and free swellrate, should not be unduly decreased in the recycling process, whereinthe superabsorbent polymer particles are separated from a solidifiedthermoplastic composition.

SUMMARY OF THE INVENTION

The invention refers to an absorbent core comprising superabsorbentpolymer particles. A part of the superabsorbent polymer particles arerecycled superabsorbent polymer particles, the recycling comprisesseparating contaminated superabsorbent polymer particles from asolidified thermoplastic composition.

The invention also refers to the use of superabsorbent polymer particlesin absorbent cores, wherein at least a part of the superabsorbentpolymer particles are recycled superabsorbent polymer particles.

Further, the invention is directed towards a method for separatingsuperabsorbent polymer particles from a solidified thermoplasticcomposition, the method comprising the steps of:

-   -   a) providing agglomerates of the superabsorbent polymer        particles and the solidified thermoplastic composition, wherein        at least a part of the superabsorbent polymer particles are        adhered to at least a part of the solidified thermoplastic        composition,    -   b) subjecting the agglomerates to a supercritical fluid        comprising carbon dioxide, propane or mixtures thereof.

The UPM value of the separated superabsorbent polymer particles obtainedby the method does not decrease by more than 40% while thesuperabsorbent polymer particles are subjected to steps a) and b).

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a plan view of a diaper as an example for an absorbent articleof the present invention.

FIG. 2 is a partial cross-sectional side view of a suitable permeabilitymeasurement system for conducting the Urine Permeability MeasurementTest.

FIG. 3 is a cross-sectional side view of a piston/cylinder assembly foruse in conducting the Urine Permeability Measurement Test.

FIG. 4 is a top view of a piston head suitable for use in thepiston/cylinder assembly shown in FIG. 3.

FIG. 5 is a cross-sectional side view of the piston/cylinder assembly ofFIG. 3 placed on fritted disc for the swelling phase.

FIG. 6 is a diagram showing the state of a pure substance, plottingpressure versus temperature.

DETAILED DESCRIPTION OF THE INVENTION Definitions

“Absorbent article” refers to devices that absorb and contain bodyexudates, and, more specifically, refers to devices that are placedagainst or in proximity to the body of the wearer to absorb and containthe various exudates discharged from the body. Absorbent articles mayinclude diapers, pants, training pants, adult incontinenceundergarments, sanitary napkin, and the like. As used herein, the term“body fluids” or “body exudates” includes, but is not limited to, urine,blood, vaginal discharges, breast milk, sweat and fecal matter.Preferred absorbent articles of the present invention are diapers,pants, training pants and/or sanitary napkins.

“Absorbent core” means a structure typically disposed between a topsheetand a backsheet of an absorbent article for absorbing and containingliquid received by the absorbent article. The absorbent core typicallycomprises absorbent material such as airfelt (comprising cellulosefibers), superabsorbent polymer particles (hereinafter referred to asSAP particles) and possibly nonwoven webs. In one embodiment, theabsorbent core may comprise less than 10% of cellulose fibers or mayeven be substantially cellulose free (i.e. less than 1% cellulose) andmay comprise one or more substrates, SAP particles disposed on the oneor more substrates, and a solidified thermoplastic composition. Thesolidified thermoplastic composition is applied on the SAP particles andat least a portion of the one or more substrates for immobilizing theSAP particles on the one or more substrates. The one or more substratesmay comprise or consist of nonwoven webs. The nonwoven webs will atleast partially surround the SAP particles and the solidifiedthermoplastic composition and these nonwovens are therefore oftenreferred to as core wrap or core cover. The core wrap or core cover mayconsist of an upper layer towards the body-facing surface of theabsorbent article and of a lower layer towards the garment-facing sideof the absorbent article. The two layers may be continuously orintermittently bonded to each other around their perimeters. The upperand lower layer may be made of the same nonwoven webs or may be made ofdifferent nonwoven webs, i.e. the upper layer may be fluid perviouswhereas the lower layer may be fluid impervious. The core wrap/corecover may also consist of a single nonwoven web, which envelops the SAPparticles and the solidified thermoplastic composition. In a multilayerabsorbent core, one or more layers of a substrate (e.g. a nonwoven web)may additionally be placed within the absorbent core to at leastpartially separate and segment the SAP particles.

In the present invention, the absorbent cores will typically comprisesmore than 80% of SAP particles by weight of absorbent material (i.e.excluding any substrate layers), more preferably more than 90%. Theabsorbent core may even be free of airfelt. The absorbent material ofthe absorbent core may also consist solely of SAP particles.

In one embodiment, the absorbent core, in addition to the SAP particles,comprises an odor control compound. The odor control compound may beprovided in the form of odor control particles. The odor controlparticles may be distributed homogeneously throughout the absorbent coreor may, alternatively, be provided only in distinct areas, while otherareas are free from odor control particles. For example, the odorcontrol particles may be provided in the form of one or more distinctlayers within the absorbent core. The odor control particles may have aparticle size similar to the particle size of the SAP particles. In oneembodiment, the odor control compound, e.g. the odor control particles,comprise tetra acetyl ethylene diamine and percarbonate. The odorcontrol particles comprising percarbonate and tetra acetyl ethylenediamine may be comprised in an amount from 200 mg to 400 mg perabsorbent core, preferably from 250 mg to 350 mg. Typically the weightof the SAP particles in the absorbent core will be from 30 times to 50times the weight of the odor control compounds, preferably the weight ofthe SAP particles in the absorbent core will be from 35 times to 45times the weight of the odor control compounds.

It is understood that for the present invention the solidifiedthermoplastic composition—as well as the odor control compound, ifpresent—will not be considered to be a comprised by the absorbentmaterial, as the solidified thermoplastic composition does not haveabsorbing properties. Further, for the present invention, the absorbentcore does not include the topsheet, the backsheet and (if present) theacquisition system of the absorbent article.

“Superabsorbent polymer particles” (“SAP particles) as used herein referto cross linked polymeric materials that can absorb at least 5 timestheir weight of an aqueous 0.9% saline solution as measured using theCentrifuge Retention Capacity test (Edana 441.2-01). The SAP particlesare in particulate form so as to be flowable in the dry state. PreferredSAP particles of the present invention are made of poly(meth)acylic acidpolymers. However, e.g. starch-based SAP particles are also comprisedwithin the scope of the present invention.

“Contaminated SAP particles” as used herein refers to SAP particles towhich the solidified thermoplastic composition of the present inventionis adhered.

“Recycled SAP particles” as used herein refers to SAP particles whichhave been separated from a solidified thermoplastic composition to whichthe SAP particles have been previously adhered. The SAP particles arepreferably separated from the solidified thermoplastic composition byuse of supercritical fluid, such as carbon dioxide, propane or mixturesthereof.

“Non-recycled SAP particles” as used herein refers to SAP particleswhich previously have not been separated from a solidified thermoplasticcomposition. The non-recycled SAP particles have preferably not beenincorporated in any absorbent articles or in parts of absorbent articles(such as in absorbent cores) before they are used in the absorbentarticles of the present invention. However, in certain embodiments, thenon-recycled SAP particles have been regained from absorbent articles,wherein they have incorporated together with absorbent fibers andwherein the SAP particles have been immobilized only due to the closeproximity to the absorbent fibers. The SAP particles are neither affixedto these absorbent fibers nor are they affixed to each other or to othermaterials (such as nonwoven webs) of the absorbent article. Examples ofsuch absorbent articles are disposable diapers containing relativelylarge amounts of absorbent fibers in addition to the SAP particles.

“Airfelt” is used herein to refer to comminuted wood pulp, which is aform of cellulose fibers (absorbent fibers).

“Comprise,” “comprising,” and “comprises” are open ended terms, eachspecifies the presence of what follows, e.g., a component, but does notpreclude the presence of other features, e.g., elements, steps,components known in the art, or disclosed herein.

“Disposable” is used in its ordinary sense to mean an article that isdisposed or discarded after a limited number of usage events overvarying lengths of time, for example, less than about 20 events, lessthan about 10 events, less than about 5 events, or less than about 2events. A disposable absorbent article is most often disposed aftersingle use.

“Diaper” refers to an absorbent article generally worn by infants andincontinent persons about the lower torso so as to encircle the waistand legs of the wearer and that is specifically adapted to receive andcontain urinary and fecal waste.

“Pant” or “training pant”, as used herein, refer to disposable garmentshaving a waist opening and leg openings designed for infant or adultwearers. A pant may be placed in position on the wearer by inserting thewearer's legs into the leg openings and sliding the pant into positionabout a wearer's lower torso. A pant may be preformed by any suitabletechnique including, but not limited to, joining together portions ofthe article using refastenable and/or non-refastenable bonds (e.g.,seam, weld, adhesive, cohesive bond, fastener, etc.). A pant may bepreformed anywhere along the circumference of the article (e.g., sidefastened, front waist fastened). While the terms “pant” or “pants” areused herein, pants are also commonly referred to as “closed diapers,”“prefastened diapers,” “pull-on diapers,” “training pants,” and“diaper-pants”.

A “nonwoven web” is a manufactured sheet, web or batt of directionallyor randomly orientated fibers, bonded by friction, and/or cohesionand/or adhesion, excluding paper and products which are woven, knitted,tufted, stitch-bonded incorporating binding yarns or filaments, orfelted by wet-milling, whether or not additionally needled. The fibersmay be of natural or man-made origin and may be staple or continuousfilaments or be formed in situ. Commercially available fibers havediameters ranging from less than about 0.001 mm to more than about 0.2mm and they come in several different forms such as short fibers (knownas staple, or chopped), continuous single fibers (filaments ormonofilaments), untwisted bundles of continuous filaments (tow), andtwisted bundles of continuous filaments (yarn). Nonwoven webs can beformed by many processes such as meltblowing, spunbonding, solventspinning, electrospinning, carding and airlaying. The basis weight ofnonwoven webs is usually expressed in grams per square meter (gsm).

Absorbent Articles

In the following, a disposable diaper will be described as one exampleof an absorbent article of the present invention. It is howeverunderstood, that other disposable absorbent articles are alsoencompassed by the present invention, especially pants, training pantsand sanitary napkins.

It should be understood, that the absorbent articles described hereinmay on the one hand be the articles, from which the SAP particles arerecycled by separating them from a solidified thermoplastic composition.On the other hand, the absorbent articles described herein may be thearticles, which comprise the absorbent cores of the present invention.These absorbent cores comprise recycled SAP particles.

FIG. 1 is a plan view of a diaper 210 according to a certain embodimentof the present invention. The diaper 210 is shown in its flat out,uncontracted state (i.e. without elastic induced contraction) andportions of the diaper 210 are cut away to more clearly show theunderlying structure of the diaper 210. A portion of the diaper 210 thatcontacts a wearer is facing the viewer in FIG. 1. The diaper 210generally may comprise a chassis 212 and an absorbent core 214 disposedin the chassis 212.

The chassis 212 of the diaper 210 in FIG. 1 comprises the main body ofthe diaper 210.

The chassis 212 may comprise an outer covering 216 including a topsheet218, which may be liquid pervious, and/or a backsheet 220, which may beliquid impervious. The absorbent core 214 may be encased between thetopsheet 218 and the backsheet 220. The chassis 212 may also includeside panels 222, elasticized leg cuffs 224, and an elastic waist feature226.

The leg cuffs 224 and the elastic waist feature 226 may each typicallycomprise elastic members 228. One end portion of the diaper 210 isconfigured as a first waist region 230 of the diaper 210. An oppositeend portion of the diaper 210 is configured as a second waist region 232of the diaper 210. An intermediate portion of the diaper 210 isconfigured as a crotch region 234, which extends longitudinally betweenthe first and second waist regions 230 and 232. The waist regions 230and 232 may include elastic elements such that they gather about thewaist of the wearer to provide improved fit and containment (elasticwaist feature 226). The crotch region 234 is that portion of the diaper210 which, when the diaper 210 is worn, is generally positioned betweenthe wearer's legs.

The diaper 210 is depicted in FIG. 1 with its longitudinal axis 236 andits transverse axis 238. The periphery 240 of the diaper 210 is definedby the outer edges of the diaper 210 in which the longitudinal edges 242run generally parallel to the longitudinal axis 236 of the diaper 210and the end edges 244 run between the longitudinal edges 242 generallyparallel to the transverse axis 238 of the diaper 210. The diaper 220may also include such other features as are known in the art includingfront and rear ear panels, waist cap features, elastics and the like toprovide better fit, containment and aesthetic characteristics.

In order to keep the diaper 210 in place about the wearer, at least aportion of the first waist region 230 may be attached by the fasteningmember 246 to at least a portion of the second waist region 232 to formleg opening(s) and an article waist. To this end, according to certainembodiments, the diaper 210 may be provided with a re-closable fasteningsystem or may alternatively be provided in the form of a pant-typediaper. When the absorbent article is a diaper, it may comprise are-closable fastening system joined to the chassis for securing thediaper to a wearer. The fastening system may include at least onefastening member 246 and at least one landing zone 248. When theabsorbent article is a pant-type diaper, the article may comprise twoside panels on each waist region 230, 232 joined to the chassis alongthe longitudinal edges of the side panels which face towards thelongitudinal axis 236. The side panels of the first waist region 230 arefurther joined to the respective side panels of the second waist region232 along their longitudinal edges facing away from the longitudinalaxis 236 to form a pant.

Taking a cross section of FIG. 1 along the sectional line 2-2 of FIG. 1and starting from the wearer facing side, the diaper 210 may comprisethe topsheet 218, the components of the absorbent core 214, and thebacksheet 220. Diaper 210 also comprises an acquisition system 250disposed between the liquid permeable topsheet 218 and the wearer facingside of the absorbent core 214. The acquisition system 250 may be indirect contact with the absorbent core.

The acquisition system 250 may comprise a single layer or multiplelayers, such as an upper acquisition layer 252 facing towards the wearerand a lower acquisition 254 layer facing the garment of the wearer.According to a certain embodiment, the acquisition system 250 mayfunction to receive a surge of liquid, such as a gush of urine. In otherwords, the acquisition system 250 may serve as a temporary reservoir forliquid until the absorbent core 214 can absorb the liquid.

In a certain embodiment, the acquisition system 250 may comprisechemically cross-linked cellulose fibers and/or nonwoven webs.

The absorbent cores of the present invention may comprise SAP particles,wherein a part of the SAP particles are recycled. Recycling the SAPparticles comprises separating contaminated superabsorbent polymerparticles from a solidified thermoplastic composition. Preferably, thecontaminated SAP particles are separated from the solidifiedthermoplastic composition by using a supercritical fluid comprisingcarbon dioxide, propane or mixtures thereof. Alternatively, thecontaminated SAP particles can be separated from the solidifiedthermoplastic composition using Soxhlet extraction.

The recycled SAP particles preferably are more than 1 weight-%, morepreferably more than 5 weight-% of the total amount of SAP particlescomprised by the absorbent core. The recycled SAP particles may be lessthan 70 weight-%, preferably less than 50 weight-%, and still morepreferably less than 50 weight-% or less than 20 weight-% of the totalamount of SAP particles comprised by the absorbent core. In the mostpreferred embodiment, the recycled SAP particles are less than 15weight-% of the total amount of SAP particles comprised by the absorbentcore.

The remaining part of the SAP particles within the absorbent core isnon-recycled SAP particles. Preferably, the recycled superabsorbentpolymer particles and the non-recycled superabsorbent polymer particleshave been mixed with each other prior to incorporating them in theabsorbent core.

The absorbent cores comprising the recycled SAP particles are preferablycomprised in absorbent articles selected from diapers, training pants,and sanitary napkins. These absorbent articles may further comprise SAPparticles in other components of the article, such as the acquisitionsystem. The SAP particles comprised in the acquisition system may partlybe recycled SAP particles.

Certain embodiments of the present invention refer to absorbent corescomprising SAP particles, wherein at least a part of the SAP particlesare recycled SAP particles. These absorbent cores are not comprisedwithin absorbent articles. Rather, the absorbent cores may be soldseparately, e.g. for replacing used absorbent cores in an absorbentarticle.

Supercritical Fluids

When a gas is compressed to a sufficiently high pressure, it becomesliquid. If, on the other hand, the gas is heated beyond a specifictemperature, it can no longer be transferred to the liquid state bycompression. This temperature is called the critical temperature and thecorresponding vapor pressure is called the critical pressure. Thesevalues of temperature and pressure define a critical point, which isunique to a given substance. The state of the substance is calledsupercritical state when both the temperature and pressure exceed thecritical point values, as shown in FIG. 6. Critical temperature andpressure values for carbon dioxide are 31.1° C. and 73.8 bar. Forpropane, the critical temperature and pressure values are 38.8° C. and42.5 bar.

This supercritical fluid (SCF) takes on many of the properties of bothgas and liquid. In the supercritical state, increasing the solventcapacity and varying the solvent properties can be achieved withrelatively small changes in temperature and pressure. Due to itsfavorable diffusivity, viscosity, surface tension and other physicalproperties, SCFs are especially suitable as solvents for extraction. Forexample SC carbon dioxide has much higher diffusion rates andconsiderably higher viscosity compared to typical liquid solvents, suchas ethanol, iso-propanol, or n-hexane.

Its low viscosity and low surface tension enable SCFs to penetrate asolid substance from which an active component is to be extracted.

Furthermore, in SCF extraction with CO₂, there is no solvent residue inthe extract. For the present invention, CO₂ purity should be at least99.95%. Also, its near ambient critical temperature makes it ideallysuitable for thermo labile products. Due to its very low latent heat ofvaporization, relatively low energy input is required for the extractseparation. Furthermore the energy required for attaining thesupercritical state of CO₂ is often less than the energy associated withdistillation of conventional organic solvents. CO₂ required for thesupercritical fluid extraction process is readily available, as it ise.g. obtained as a by-product from the fermentation process orfertilizer industry. So its use as an extractant does not cause anyfurther increase in the amount of CO₂ present in the atmosphere. Thereis no additional “Green House effect” from using CO₂ as the SCF solvent.Moreover, CO₂ is readily available at low cost.

Method for Obtaining Recycled SAP Particles

The system used for carrying out the method of the present inventioncomprises at least one extractor, one precipitator and tubes connectingthe extractor and the precipitator. Furthermore, the system shouldcomprise a device, such as a pump, which maintains constant flow-rateand pressure of the supercritical fluid within the system. Allcomponents need to be combined in a closed system. The SCF passesthrough the extractor, leaves the extractor through at least one outlet(of the extractor) into the tubes and moves on to the precipitatorthrough at least one inlet (of the precipitator). Upon expansion in theprecipitator, the expanded gas (former SCF) leaves the precipitatorthrough at least one outlet (of the precipitator) and passes back to theextractor through tubes. Before entering the extractor again through atleast one inlet (of the extractor), the gas needs to be compressed totransfer it back into its supercritical state. Valves may serve toenable decoupling of the different components (e.g. extractor,precipitator) such that the extractor and/or precipitator can beisolated from the closed system to allow opening of these componentswithout subjecting the complete system to ambient conditions.Optionally, the system may further comprise coolers (e.g. to cool theprecipitator and/or to cool the gas within the tubes before it istransformed back to its supercritical state). The system may alsocomprise a heating device to maintain the supercritical fluid at thedesired temperature.

To recycle the SAP particles, the SAP particles are placed in anappropriate container, herein called an extractor. At least a part ofthe SAP particles placed in the extractor are closely adhered to asolidified thermoplastic composition comprising at least 30 weight-% ofa thermoplastic polymer based on the weight of the solidifiedthermoplastic composition. In most embodiments, the majority (i.e. morethan 50%) of the SAP particles will be closely adhered to the solidifiedthermoplastic composition. However, more than 50%, e.g. more than 70% ormore than 80% may be closely adhered to the solidified thermoplasticcomposition, or even more than 95%. To be closely adhered, it issufficient that a relatively small part of the surface of the SAPparticles has the solidified thermoplastic composition adhered to itwhile the remaining surface is free of the solidified thermoplasticcomposition. For the present invention such SAP particles will alreadyregarded as being contaminated with the solidified thermoplasticcomposition. Typically, the SAP particles will be immobilized within afibrous network of the solidified thermoplastic composition.

As the name already indicates, the extractor, wherein the contaminatedSAP particles are placed, serves as an extraction vessel. The extractormay e.g. be an autoclave. The extractor needs to be hermeticallysealable against ambient air to allow the appropriate pressure andtemperature to build up.

The material placed in the extractor may be only the SAP particles towhich solidified thermoplastic composition is adhered. However, it hasbeen surprisingly found that the method of the present invention canalso be carried out when the SAP particles with the closely adheredsolidified thermoplastic composition are comprised within an absorbentcore of an absorbent article while being subjected to the method of thepresent invention. The absorbent core may further to the contaminatedSAP particles comprise nonwoven webs, airfelt and/or other liquidabsorbing materials, such as absorbent foams. In one embodiment, theabsorbent core comprises the contaminated SAP particles and one or morenonwoven webs.

In one embodiment, the absorbent core subjected to the method of thepresent invention will comprise at least 75 weight-% of SAP particlesbased on the total weight of the absorbent core. In another embodiment,the absorbent core will comprise at least 80 weight-% of SAP particlesbased on the total weight of the absorbent core. In still anotherembodiment, the absorbent core will comprise at least 90 weight-% of SAPparticles based on the total weight of the absorbent core.

Further, in one embodiment, the absorbent core subjected to the methodof the present invention will comprise less than 8 weight-% of thesolidified thermoplastic composition based on the total weight of theabsorbent core. In another embodiment, the absorbent core will compriseless than 6 weight-% of the solidified thermoplastic composition basedon the total weight of the absorbent core. In still another embodiment,the absorbent core will comprise less than 5 weight-% of the solidifiedthermoplastic composition based on the total weight of the absorbentcore.

Alternatively, the material subjected to the method of the presentinvention comprises further to the absorbent cores with the contaminatedSAP particles also other components of an absorbent article, such as theacquisition system.

Moreover, the inventors of the present invention have found thatcomplete absorbent articles, e.g. complete diapers, can be subjected tothe method of the present invention. This eliminates the need toretrieve the absorbent cores from the absorbent articles beforesubjecting them to the method of the present invention. Thus, in a stillfurther embodiment, complete absorbent articles, such as disposablediapers, training pants or sanitary napkins, are subjected to the methodof the present invention. These absorbent articles comprise the SAPparticles to which the solidified thermoplastic composition is adhered.The SAP particles are comprised inside the absorbent articles, i.e. theSAP particles with the adhered solidified thermoplastic composition aresurrounded by other materials, such as nonwoven webs, films and/orairfelt. The complete absorbent articles may also comprise inks whichhave been used to provide a print on portions of the absorbent article(e.g. on the backsheet or the landing zone).

In one embodiment, the disposable absorbent article subjected to themethod of the present invention comprises at least 25 weight-% of SAPparticles based on the total weight of the disposable absorbent article.In another embodiment, the disposable absorbent article comprises atleast 30 weight-% of SAP particles based on the total weight of thedisposable absorbent article.

Further, in one embodiment, the disposable absorbent article subjectedto the method of the present invention will comprise less than 3weight-% of the solidified thermoplastic composition based on the totalweight of the disposable absorbent article. In another embodiment, thedisposable absorbent article will comprise less than 2.5 weight-% of thesolidified thermoplastic composition based on the total weight of thedisposable absorbent article. After the SAP particles with the adheredsolidified thermoplastic composition have been placed in the extractor,at least one inlet and at least one outlet is connected to the extractorand the extractor is hermetically sealed against ambient air.

Supercritical fluid, such as supercritical carbon dioxide, is fed intothe system and enters the extractor through the at least one inlet line.While passing through the extractor, the supercritical fluid also passesthrough the material comprised in the extractor.

Due to its low viscosity and high diffusion coefficient, thesupercritical fluid can easily penetrate the material placed in theextractor, thus coming into close contact with the SAP particles towhich the solidified thermoplastic composition is adhered, even if theSAP particles are comprised in an absorbent article. Passing though thematerial, the supercritical fluid extracts the solidified thermoplasticcomposition, which thereby is removed from the SAP particles little bylittle.

The supercritical fluid together with the extracted solidifiedthermoplastic composition leaves the extractor through the at least oneoutlet and passes through tubes into the precipitator. In theprecipitator the supercritical fluid is allowed to expand to conditionsbelow the supercritical temperature and pressure, e.g. supercriticalcarbon dioxide and/or propane is/are transferred back to the gaseousstate. Upon expansion of the supercritical fluid, the extractedsolidified thermoplastic composition precipitates in the precipitationvessel, as the gaseous carbon dioxide and/or propane can no longer serveas an extraction medium.

However, the chemical configuration of the solidified thermoplasticcomposition will most likely not be the same as the chemicalconfiguration, which the solidified thermoplastic composition had whileit was adhered to the SAP particles. For example, if the solidifiedthermoplastic composition is not a pure chemical compound but rather amixture of different components, the different components may have atleast partly been separated from each other upon extraction, possiblyresulting in part of the formerly solidified thermoplastic compositionbeing now in a liquid state (e.g. oil, if present).

Upon precipitation of the extracted material in the precipitator, thecarbon dioxide and/propane is regenerated, i.e. not “loaded” with theextracted material any longer. The carbon dioxide and/or propane leavethe precipitator through at least one outlet and enter into the pipeleads it back to the precipitator. At its way back, the gas iscompressed again until it has reached its supercritical state.Thereupon, the supercritical fluid can again enter the extractor whereinthe SAP particles with the adhered solidified thermoplastic compositionhave been placed. As has been explained, the method of the presentinvention can be carried out in a closed system, where the carbondioxide and/or the propane can be at least partially recycled and bere-used for many cycles, passing through the extractor with thecontaminated SAP particles again and again.

Pressure and Temperature

As higher pressures are more difficult to facilitate, relatively lowpressures are desirable from a process engineering and cost standpoint.However, it has been found that a relatively high pressure may make themethod of the invention more efficient, possibly leading to a shortertime, during which the contaminated SAP particles have to be subjectedto the supercritical fluid in order to remobilize SAP particles and freethem from the solidified thermoplastic composition. Higher pressuremeans that more molecules of the supercritical fluid are present pergiven volume, thus enabling faster extraction. In the method of thepresent invention, the supercritical fluid may be under a pressure offrom 100 bar to 600 bar, or from 150 bar to 450 bar or from 200 bar to400 bar, or from 200 bar to 375 bar.

As carbon dioxide reaches its supercritical state at a pressure of 73.8bar and at a temperature of 31.1° C., the temperature of thesupercritical fluid should be at least 40° C. Temperatures below 40° C.may result in areas within the system having a temperature which is atleast temporarily below the supercritical temperature of 31.1° C. Thus,to ensure process stability, the temperature should be at least 40° C.However, if propane is used as supercritical fluid (or a mixture whichpredominantly consists of propane), it may be desirable to have atemperature of at least 45° C. due to the slightly higher criticaltemperature of propane compared to carbon dioxide. Generally, it isdesirable that the temperature of the supercritical fluid is from 40° C.to 100° C., preferably from 40° C. to 75° C. and more preferably from40° C. to 60° C. Temperatures above 100° C. do not only increase thecost for running the system, but they may also have an adverse effect onthe SAP particles, e.g. yellowing of the SAP particles.

If the contaminated SAP particles subjected to the method of theinvention comprise odour control compounds, such as odour controlparticles comprising percarbonate and tetra acetyl ethylene diamine, theodour control compound may deteriorate at elevated temperatures. Forexample, percarbonate may decompose, setting free hydrogen peroxide.However, for the present invention it is not critical whether the odorcontrol compound decomposes and is inactivated upon being subjected tothe present invention, as long as the SAP particles are not adverselyaffected.

If it is desired to maintain activity of the odor control compounds, thetemperature, upon which the odor control compounds are deactivated canbe determined and the temperature, at which the contaminated SAPparticles comprising the odor control compounds, are subjected tosupercritical fluid, can be chosen accordingly to avoid deactivation (aslong as no temperature below 40° C. is required—in these embodiments theactivity of the odor control compound cannot be maintained). Forexample, percarbonate should not be subjected to temperatures above 60°C. in order to avoid decomposition and liberation of hydrogen peroxide.

Amount of Supercritical Fluid and Time

The supercritical fluid is provided to the extractor comprising thecontaminated SAP particles as a continuous stream. The stream enters theextractor through the at least one inlet and leaves the extractorthrough the at least one outlet.

Generally, it is desirable that the amount of supercritical fluid ismany times the amount of solidified thermoplastic composition, which isto be extracted in order to separate the solidified thermoplasticcomposition from the SAP particles.

The amount which is actually needed inter alia depends on whether or notco-solvents are applied besides the carbon dioxide and/or propane. Ifco-solvents are used, lower amounts of supercritical fluid may besufficient. If pure carbon dioxide is used, the amount of supercriticalfluid to flow through the extractor is desirable from 50 time to 500times (by weight), more preferably from 70 times to 150 times (byweight) the amount of the solidified thermoplastic composition.

If pure propane or a mixture of (only) carbon dioxide and propane (i.e.with no additional co-solvent) is used, the amount of supercriticalfluid to flow through the extractor is desirable from 40 time to 300times (by weight), more preferably from 50 times to 100 times (byweight) the amount of the solidified thermoplastic composition. If amixture of carbon dioxide and propane is used, it is preferred that themixture consists of from 60 weight-% to 95 weight-% of carbon dioxideand from 5 weight-% to 40 weight-% of propane based on the total weightof supercritical fluid, more preferably of from 75 weight-% to 95weight-% of carbon dioxide and from 5 weight-% to 25 weight-% ofpropane.

If co-solvents are used, it may be sufficient to use from 20 times to120 times (by weight) the amount of supercritical fluid to flow throughthe extractor compared to the amount of solidified thermoplasticcomposition, preferably from 20 times to 80 times (by weight) and morepreferably from 20 times to 60 times.

The time, for which the contaminated SAP particles have to be subjectedto the supercritical fluid treatment in order to separate the SAPparticles from the solidified thermoplastic composition will inter aliadepend on the pressure of the supercritical fluid, on the flow rate andon which supercritical fluid is used.

The contaminated SAP particles may generally be subjected to thesupercritical fluid for from 15 minutes to 180 minutes, or from 30minutes to 90 minutes.

The method of the present invention may be carried out in a batchprocess or in a quasi-continuous process. A “batch process” as usedherein means that a given amount of SAP particles with adheredsolidified thermoplastic composition is placed in the extractor andtreated with supercritical fluid until the SAP particles have beencompletely separated from the solidified thermoplastic composition.Thereafter, the SAP particles (and other parts of the disposableabsorbent articles/complete absorbent articles, if present) are takenout of the extractor and a new amount of SAP particles with adheresolidified thermoplastic composition (i.e. a new batch) is placed in theextractor. Also, it may be necessary to empty the precipitator, if thereis too much precipitated material resulting from extraction of thesolidified thermoplastic composition. However, the present inventionalso encompasses methods wherein the SAP particles are treated in aquasi-continuous process. “Quasi-continuous” as used herein means thatmore than one extractor is comprised by the system. The system is set upappropriately to allow one or more extractors to be disengaged from thesystem such that they can be opened while leaving the remainingsystem—with the other extractor(s)—unaffected.

Supercritical Fluid Used in the Method of the Present Invention

For the present invention, the supercritical fluid will comprise carbondioxide, propane or mixtures thereof. Both, carbon dioxide and propaneare non-polar solvents.

In general the extractability of the compounds with a SCF depends on theoccurrence of the individual functional groups in these compounds, theirmolecular weights and polarity.

Many non-polar organic solvents (such as carbon dioxide or propane) areable to dissolve polar substances. When comparing a polar and non-polarmolecule with similar molar masses, the polar molecule generally has ahigher boiling point, because of the dipole-dipole interaction betweenpolar molecules. The most common form of such polar interaction is thehydrogen bond, which is also known as the H-bond.

In order to further improve the solving power of the SCF used in themethod of the present invention, one or more co-solvent may be used inaddition to the carbon dioxide, propane or carbon dioxide/propanemixture. Thus, in one embodiment of the present invention, the SCFcomprises one or more co-solvents in addition to the carbon dioxide,propane or carbon dioxide/propane mixture. Also, in one embodiment ofthe present invention, the SCF is a mixture of carbon dioxide and one ormore co-solvents. In an alternative embodiment of the present invention,the SCF consists of carbon dioxide.

The co-solvents for use in the method of the present invention andcomprised by the SCF, which is provided to the extractor may be selectedfrom the group consisting of ethanol, ethyl acetate, butane, butylacetate, acetone, nitrous oxide, carbon dioxide, nitrogen, water, andmixtures thereof. The amount of the co-solvent (or the total amount ofco-solvents, if more than one co-solvent is used) comprised by the SCFwhich is provided to the extractor may be from 0.1 weight-% to 40weight-%, preferably from 0.5 weight-% to 30 weight-%, and morepreferably from 1 weight-% to 20 weight-% based on the total weight ofsupercritical fluid. All supercritical fluids are completely misciblewith each other so for a mixture a single phase can be guaranteed if thecritical point of the mixture is exceeded.

It has been found that it is not only possible to carry out the methodof the present invention with complete absorbent cores and even withcomplete absorbent articles comprising the absorbent cores.Surprisingly, it has been further found that the method may even workbetter if complete absorbent cores or complete or at least partiallyassembled absorbent articles are used.

Without wishing to be bound by theory, it is believed that one reasonfor this improvement is that certain compounds comprised by theabsorbent core or absorbent article act as co-solvents. For example,absorbent articles typically comprise adhesives which are used to bondthe different webs and materials of the article to each other. Moreover,many absorbent articles have elastic members, which may comprisesubstances useful as co-solvents. Other compounds, which often find usein absorbent articles, are surfactants (e.g. to render the topsheethydrophilic). Such surfactants may also work as co-solvents for themethod of the invention. It should be understood that for the presentinvention these “inherent co-solvents” are not taken into considerationwhen referring to co-solvents, which are used in the supercritical fluid(especially when determining preferred compounds and amounts ofco-solvents). Instead, when referring to co-solvents, only thosecompounds are referred to, which are consciously and in a controlledmanner, mixed into the supercritical fluid.

The SCF does not only penetrate through the contaminated SAP particlesbut penetrates through the absorbent article as a whole. Thus, not onlythe solidified thermoplastic composition is extracted, but also othercompounds, such as adhesives used in other areas of the article,surfactants, inks and possible elastifiers in elastic elements areaffected by extraction. This can be easily demonstrated by the fact,that the absorbent article is—at least to a certain degree-demounted anddeconstructed into its individual elements, such as topsheet, backsheet,tapes etc., which have formerly be assembled into the absorbent article.

Thus, as other compounds are extracted, they are set free and arecomprised in the stream of SCF, passing with the SCF through theextractor, thereby also coming into contact with the contaminated SAPparticles. Contrary to supercritical CO2 and propane, many of thesecompounds are polar substances, which may support extraction of thesolidified thermoplastic composition, especially if the solidifiedthermoplastic composition comprises substances (i.e. substancesadditionally to the polymer of the solidified thermoplasticcomposition), which are rather polar. However, rather non-polarcompounds extracted from the absorbent core or absorbent article ofcourse also have the potential of a co-solvent.

Alternatively to the method set out above, the recycled SAP particlescan be obtained from contaminated SAP particles by Soxhlet extraction asis well known in the art. Suitable solvents for Soxhlet extraction arehexan, chloroform, acetone or ethylacetate.

Solidified Thermoplastic Composition

The solidified thermoplastic composition of the present invention, whichis adhered to the SAP particles, may be an adhesive, preferably a hotmelt adhesive. The adhesive may have been initially applied toimmobilize the SAP particles. Such immobilization of the SAP particlesmay generally be required in embodiments, wherein the absorbent core ofa disposable absorbent article comprises little (e.g. less than 10% bytotal weight of the absorbent material) of airfelt or wherein theabsorbent core comprises no airfelt at all. Typically, the SAP particlesare laid down on a nonwoven carrier web, where they are immobilized toensure they stay in place during manufacture, storage and use of theabsorbent article.

It should be understood that the solidified thermoplastic compositionmay not be in its solidified state during application onto the SAPparticles but the solidified thermoplastic composition may be heated upto a temperature where it is semi-fluid or fluid in order to facilitateapplication on the SAP particles. Thus, a solidified thermoplasticcomposition in the present invention refers to a composition which issolidified at room temperature. Generally, the solidified thermoplasticcomposition in the present invention should also be solid at andslightly above in-use temperatures of absorbent articles, i.e. at atemperature up to about 40° C. (even though parts of the absorbentarticle will have lower in-use temperatures). The solidifiedthermoplastic composition readily immobilizes the SAP particles andholds them in place.

The solidified thermoplastic composition may at least partly be appliedin fibrous form onto the SAP particles (e.g. by spraying) while thesolidified thermoplastic composition has been transferred into asemi-fluid or fluid state (upon heating) to form a kind of a fibrousadhesive-network around the SAP particles. If the solidifiedthermoplastic composition is applied in fibrous form, the fibers willtypically have an average thickness of about 1 to about 50 micrometersor about 1 to about 35 micrometers and an average length of about 5 mmto about 50 mm or about 5 mm to about 30 mm.

The solidified thermoplastic composition may comprise a singlethermoplastic polymer or a blend of thermoplastic polymers. Thethermoplastic polymer(s) may have a softening point, as determined bythe ASTM Method D-36-95 “Ring and Ball”, in the range between 50° C. and300° C., The thermoplastic polymer(s) preferably have a molecular weight(weight average Mw in Dalton) of more than 10,000 and a glass transitiontemperature (Tg) below room temperature (25° C.) or −6° C.>Tg<16° C.Typical concentrations of the thermoplastic polymer(s) in the solidifiedthermoplastic composition are in the range of 30 weight-% to about 50weight-% by weight, preferably 30 weight-% to about 40 weight-% byweight. Preferably, the thermoplastic polymers of the solidifiedthermoplastic composition are immiscible with water (in amounts above 5%by weight of the solidified thermoplastic composition).

Exemplary thermoplastic polymers are block copolymers—such as styrenicblock copolymers—including A-B-A triblock structures, A-B diblockstructures and (A-B)n radial block copolymer structures wherein the Ablocks are non-elastomeric polymer blocks, typically comprisingpolystyrene, and the B blocks are unsaturated conjugated diene or(partly) hydrogenated versions of such. The B block is typicallyisoprene, butadiene, ethylene/butylene (hydrogenated butadiene),ethylene/propylene (hydrogenated isoprene), and mixtures thereof.Preferably, the polymer in the solidified thermoplastic composition is astyrene-isoprene-styrene (SIS) block copolymer, astyrene-butadiene-styrene (SBS) block copolymer or mixtures thereof.Styrene-block-copolymers are often used in adhesives which findapplication in absorbent articles. In embodiments of the presentinvention wherein the solidified thermoplastic composition comprisesmore than one polymer, the solid composition preferably comprises atleast 30 weight-% of a styrene-block-copolymer, such as a styreneisoprene block copolymer, based on the total weight of the solidifiedthermoplastic composition.

Other suitable thermoplastic polymers that may be employed aremetallocene polyolefins, which are ethylene polymers prepared usingsingle-site or metallocene catalysts. Therein, at least one comonomercan be polymerized with ethylene to make a copolymer, terpolymer orhigher order polymer. Also applicable are amorphous polyolefins oramorphous polyalphaolefins (APAO) which are homopolymers, copolymers orterpolymers of C2 to C8 alpha olefins. Besides the at least 30 weight-%of the thermoplastic polymer, the solidified thermoplastic compositionmay further comprise tackifying resins and/or oils. Furthermore, thesolidified thermoplastic composition may comprise relatively smallamounts of additives, such as antioxidants, fillers (e.g. sand and/orsilicates) and/or surfactants.

The amount of tackifying resins, if present in the solidifiedthermoplastic composition, will typically be from 1 weight-% to 60weight-%, preferably from 5 weight-% to 40 weight-% and more preferablyfrom 5 weight-% to 30 weight-% based on the weight of the solidifiedthermoplastic composition. The amount of oils, if present in thesolidified thermoplastic composition, will typically be from 1 weight-%to 40 weight-%, preferably from 5 weight-% to 30 weight-%, or from 5weight-% to 20 weight-% based on the weight of the solidifiedthermoplastic composition. The solidified thermoplastic composition ofthe present invention may comprise more than one oil (i.e. differentoils) and/or may comprise more than one tackifying resin (i.e. differenttackifying resins). The overall amount of additives, if used in thesolidified thermoplastic composition, may not more than 15 weight-%,preferably not more than 10 weight-%, more preferably not more than 8weight-% based on the weight of the solidified thermoplasticcomposition.

A resin for the present invention is a hydrocarbon secretion of manyplants, particularly coniferous trees, e.g. rosin esters (which areoften used as tackifiers). The term resin herein is also used forsynthetic resins of similar properties. Synthetic resins are materialswith similar properties to natural resins—viscous liquids capable ofhardening. They are typically manufactured by esterification or soapingof organic compounds. The classic variety is epoxy resin. The tackifyingresin of the solidified thermoplastic composition has typically a weightaverage Mw (in Dalton) below 5,000. The Tg will usually be above roomtemperature. “Oil” for the present invention is any substance that isliquid at ambient temperatures and is hydrophobic but soluble in organicsolvents. Oils have a high carbon and hydrogen content and are non-polarsubstances. Oils useful for the solidified thermoplastic composition ofthe present invention are mineral oils. In one embodiment, the oil ispetrolatum oil, for example paraffinic oil, napthenic oil or mixturesthereof. The oil may have a low weight average Mw (in Dalton) of lessthan 1,000. The Tg will preferably be below room temperature (25° C.).

Examples for solidified thermoplastic compositions of the presentinvention are the following hot melt adhesives: Bostik Findley H2401, anelastic adhesive; Lunatack D 3155 B Zeropack and D 3166 Zeropack from H.B. Fuller; HL 1358 from H. B. Fuller; Dispomelt (DM526 and DM519 A) soldby National Starch.

One example of an absorbent article comprising an absorbent core withSAP particles, which have been immobilized with a solidifiedthermoplastic composition of the present invention is Pampers “Cruisers”diapers as sold by the Procter and Gamble Company in the USA in February2011. These diapers do not contain any recycled SAP particles.

Superabsorbent Polymer Particles

The SAP particles may be of numerous shapes. The term “particles” refersto granules, fibers, flakes, spheres, powders, platelets and othershapes and forms known to persons skilled in the art of SAP particles.E.g. the particles can be in the form of granules or beads, having aparticle size from about 10 μm to about 1000 μm, preferably from about100 μm to about 1000 μm, even more preferably from about 150 μm to about850 μm and most preferably from about 150 μm to about 500 μm. In anotherembodiment, the SAP particles can be in the shape of fibers, i.e.elongated, acicular SAP particles. In those embodiments, the SAP fibershave a minor dimension (i.e. diameter of the fiber) of less than about 1mm, usually less than about 500 μm, and preferably less than 250 μm downto 50 μm. The length of the fibers is preferably about 3 mm to about 100mm. The fibers can also be in the form of a long filament that can bewoven. Preferred SAP particles of the present invention arespherical-like particles. According to the present invention and incontrast to fibers, “spherical-like particles” have a longest and asmallest dimension with a particulate ratio of longest to smallestparticle dimension in the range of 1-5, where a value of 1 would equatea perfectly spherical particle and 5 would allow for some deviation fromsuch a spherical particle.

The SAP particles useful in the present invention include a variety ofwater-insoluble, but water-swellable polymers capable of absorbing largequantities of fluids. Such polymers materials are generally known in theart and include all those well-known polymers used or deemed useful inthe context of disposable absorbent article technology.

Preferred polymer materials for use in making SAP particles are slightlynetwork cross linked polymers of partially neutralized polyacrylic acidsand starch derivatives thereof. Starch-based SAP particles are alsoencompassed in the present invention. Preferably, the SAP particlescomprise from 25% to 95% by weight, more preferably from 50% to 80% byweight, neutralized, slightly network cross-linked, polyacrylic acid.Network cross-linking renders the polymer substantially water-insolubleand, in part, determines the absorptive capacity and extractable polymercontent characteristics of the hydrogel-forming absorbent polymers.

While the SAP is preferably of one type (i.e., homogeneous), mixtures ofpolymers can also be used in the present invention. The SAP particlescan also comprise mixtures with low levels of one or more additives,such as for example powdered silica, surfactants, adhesive, binders, andthe like. Furthermore, the SAP particles can comprise a gradient inparticle size or can comprise a certain range of particle size.

The SAP particles to be used in absorbent articles of the presentinvention preferably are mixtures of recycled SAP particles andnon-recycled SAP particles.

Many of the formerly known SAP particles exhibited gel blocking. “Gelblocking” occurs when particles of the SAP are wetted and the particlesswell so as to inhibit fluid transmission to other zones or regions ofthe absorbent structure. Wetting of these other regions of the absorbentcore therefore takes place via a very slow diffusion process. Inpractical terms, this means acquisition of fluids by the absorbentstructure is much slower than the rate at which fluids are discharged,especially in gush situations. Leakage from the absorbent article cantake place well before the particles of SAP in the absorbent core areeven close to being fully saturated or before the fluid can diffuse orwick past the “blocking” particles into the rest of the absorbent core.

One commonly applied way to reduce gel blocking is to make the particlesstiffer, which enables the SAP particles to retain their original shapethus creating or maintaining void spaces between the particles. Awell-known method to increase stiffness is to covalently cross-link thecarboxyl groups exposed on the surface of the SAP particles. This methodis commonly referred to as surface cross-linking.

The SAP particles may have a permeability at equilibrium expressed asUPM (Urine Permeability Measurement) value greater than 80, preferablygreater than 100. The UPM value may be less than 300, preferably lessthan 150, more preferably less than 120 UPM units, where 1 UPM unit is1×10−7 (cm³·s)/g.

The UPM value is measured according to the UPM Test method set outbelow. This method is closely related to the SFC test method of theprior art. The UPM Test method typically measures the flow resistance ofa preswollen layer of superabsorbent polymer particles, i.e. the flowresistance is measured at equilibrium. Therefore, such SAP particleshaving a high UPM value exhibit a high permeability when a significantvolume of the absorbent article is already wetted by the liquidexudates. These embodiments exhibit good absorption properties not onlyat the first gush but also at the subsequent gushes.

In some embodiments, the SAP particles may have a FSR (Free Swell Rate)of more than 0.1 g/g/s, or of from 0.1 to 2 g/g/s, preferably from 0.3to 1 g/g/s, more preferably from 0.3 to 0.6 g/g/s, even more preferablyfrom 0.4 to 0.6 g/g/s.

The Free Swell Rate of the SAP particles is measured according to theFSR test method set out below. SAP particles having high free swell ratevalues will be able to absorb liquid, relatively quickly. No externalpressure is applied to the gel bed in order to measure the free swellrate.

The SAP particles may have a CRC (centrifuge retention capacity) valueof more than 20 g/g, preferably more than 24 g/g, or of from 20 to 50g/g, preferably from 20 to 40 g/g, more preferably from 24 to 30 g/g, asmeasured according to EDANA method WSP 241.2-05. The CRC measures theliquid absorbed by the SAP particles for free swelling in excess liquid.SAP particles having a high CRC value are preferred since less SAPparticles are needed to facilitate a required overall capacity forliquid absorption.

For the present invention, the UPM value of the recycled SAP particlespreferably does not decrease by more than 40%, preferably not more than35% and still more preferably not more than 30% during the process ofrecycling contaminated SAP particles. The recycled SAP particlespreferably have an UPM value of 60% to 95% compared to the UPM value ofthe non-recycled SAP particles.

In absorbent articles of the present invention, comprising recycled andnon-recycled SAP particles, the recycled SAP particles may have an UPMvalue of at least 50 (10⁻⁷ (cm³·s/g), preferably at least 60 (10⁻⁷(cm³·s)/g) and the non-recycled SAP particles may have an UPM value ofat least 80 (10⁻⁷ (cm³·s)/g), preferably at least 100 (10⁻⁷ (cm³·s)/g).

Test Methods for Determining UPM and FSR

The following test methods can be used for non-recycled as well as forrecycled SAP particles.

Urine Permeability Measurement (UPM) Test method

Urine Permeability Measurement System

This method determined the permeability of a swollen hydrogel layer 1318formed from swollen SAP particles. The equipment used for this method isdescribed below. This method is closely related to the SFC (Salt FlowConductivity) test method of the prior art.

FIG. 2 shows permeability measurement system 1000 set-up with theconstant hydrostatic head reservoir 1014, open-ended tube for airadmittance 1010, stoppered vent for refilling 1012, laboratory jack1016, delivery tube 1018, stopcock 1020, ring stand support 1022,receiving vessel 1024, balance 1026 and piston/cylinder assembly 1028.

FIG. 3 shows the piston/cylinder assembly 1028 comprising a metal weight1112, piston shaft 1114, piston head 1118, lid 1116, and cylinder 1120.The cylinder 1120 is made of transparent polycarbonate (e.g., Lexan®)and has an inner diameter p of 6.00 cm (area=28.27 cm2) with innercylinder walls 1150 which are smooth. The bottom 1148 of the cylinder1120 is faced with a US. Standard 400 mesh stainless-steel screen cloth(not shown) that is bi-axially stretched to tautness prior to attachmentto the bottom 1148 of the cylinder 1120. The piston shaft 1114 is madeof transparent polycarbonate (e.g., Lexan®) and has an overall length qof approximately 127 mm. A middle portion 1126 of the piston shaft 1114has a diameter r of 21.15 mm. An upper portion 1128 of the piston shaft1114 has a diameter s of 15.8 mm, forming a shoulder 1124. A lowerportion 1146 of the piston shaft 1114 has a diameter t of approximately⅝ inch and is threaded to screw firmly into the center hole 1218 (seeFIG. 4) of the piston head 1118. The piston head 1118 is perforated,made of transparent polycarbonate (e.g., Lexan®), and is also screenedwith a stretched US. Standard 400 mesh stainless-steel screen cloth (notshown). The weight 1112 is stainless steel, has a center bore 1130,slides onto the upper portion 1128 of piston shaft 1114 and rests on theshoulder 1124. The combined weight of the piston head 1118, piston shaft1114 and weight 1112 is 596 g (±6 g), which corresponds to 0.30 psi overthe area of the cylinder 1120. The combined weight may be adjusted bydrilling a blind hole down a central axis 1132 of the piston shaft 1114to remove material and/or provide a cavity to add weight. The cylinderlid 1116 has a first lid opening 1134 in its center for verticallyaligning the piston shaft 1114 and a second lid opening 1136 near theedge 1138 for introducing fluid from the constant hydrostatic headreservoir 1014 into the cylinder 1120.

A first linear index mark (not shown) is scribed radially along theupper surface 1152 of the weight 1112, the first linear index mark beingtransverse to the central axis 1132 of the piston shaft 1114. Acorresponding second linear index mark (not shown) is scribed radiallyalong the top surface 1160 of the piston shaft 1114, the second linearindex mark being transverse to the central axis 1132 of the piston shaft1114. A corresponding third linear index mark (not shown) is scribedalong the middle portion 1126 of the piston shaft 1114, the third linearindex mark being parallel with the central axis 1132 of the piston shaft1114. A corresponding fourth linear index mark (not shown) is scribedradially along the upper surface 1140 of the cylinder lid 1116, thefourth linear index mark being transverse to the central axis 1132 ofthe piston shaft 1114. Further, a corresponding fifth linear index mark(not shown) is scribed along a lip 1154 of the cylinder lid 1116, thefifth linear index mark being parallel with the central axis 1132 of thepiston shaft 1114. A corresponding sixth linear index mark (not shown)is scribed along the outer cylinder wall 1142, the sixth linear indexmark being parallel with the central axis 1132 of the piston shaft 1114.Alignment of the first, second, third, fourth, fifth, and sixth linearindex marks allows for the weight 1112, piston shaft 1114, cylinder lid1116, and cylinder 1120 to be re-positioned with the same orientationrelative to one another for each measurement.

The cylinder 1120 specification details are:

Outer diameter u of the Cylinder 1120: 70.35 mm

Inner diameter p of the Cylinder 1120: 60.0 mm

Height v of the Cylinder 1120: 60.5 mm

The cylinder lid 1116 specification details are:

Outer diameter w of cylinder lid 1116: 76.05 mm

Inner diameter x of cylinder lid 1116: 70.5 mm

Thickness y of cylinder lid 1116 including lip 1154: 12.7 mm

Thickness z of cylinder lid 1116 without lip 1154: 6.35 mm

Diameter a of first lid opening 1134: 22.25 mm

Diameter b of second lid opening 1136: 12.7 mm

Distance between centers of first and second lid openings 1134 and 1136:23.5 mm

The weight 1112 specification details are:

Outer diameter c: 50.0 mm

Diameter d of center bore 1130: 16.0 mm

Height e: 39.0 mm

The piston head 1118 specification details are

Diameter f: 59.7 mm

Height g: 16.5 mm

Outer holes 1214 (14 total) with a 9.65 mm diameter h, outer holes 1214equally spaced with centers being 47.8 mm from the center of center hole1218

Inner holes 1216 (7 total) with a 9.65 mm diameter i, inner holes 1216equally spaced with centers being 26.7 mm from the center of center hole1218

Center hole 1218 has a diameter j of ⅝ inches and is threaded to accepta lower portion 1146 of piston shaft 1114.

Prior to use, the stainless steel screens (not shown) of the piston head1118 and cylinder 1120 should be inspected for clogging, holes orover-stretching and replaced when necessary. A urine permeabilitymeasurement apparatus with damaged screen can deliver erroneous UPMresults, and must not be used until the screen has been replaced.

A 5.00 cm mark 1156 is scribed on the cylinder 1120 at a height k of5.00 cm (±0.05 cm) above the screen (not shown) attached to the bottom1148 of the cylinder 1120. This marks the fluid level to be maintainedduring the analysis. Maintenance of correct and constant fluid level(hydrostatic pressure) is critical for measurement accuracy.

A constant hydrostatic head reservoir 1014 is used to deliver saltsolution 1032 to the cylinder 1120 and to maintain the level of saltsolution 1032 at a height k of 5.00 cm above the screen (not shown)attached to the bottom 1148 of the cylinder 1120. The bottom 1034 of theair-intake tube 1010 is positioned so as to maintain the salt solution1032 level in the cylinder 1120 at the required 5.00 cm height k duringthe measurement, i.e., bottom 1034 of the air tube 1010 is inapproximately same plane 1038 as the 5.00 cm mark 1156 on the cylinder1120 as it sits on the support screen (not shown) on the ring stand 1040above the receiving vessel 1024. Proper height alignment of theair-intake tube 1010 and the 5.00 cm mark 1156 on the cylinder 1120 iscritical to the analysis. A suitable reservoir 1014 consists of a jar1030 containing a horizontally oriented L-shaped delivery tube 1018 forfluid delivery, a vertically oriented open-ended tube 1010 for admittingair at a fixed height within the constant hydrostatic head reservoir1014, and a stoppered vent 1012 for re-filling the constant hydrostatichead reservoir 1014. Tube 1010 has an internal diameter of 12.5 mm±0.5mm. The delivery tube 1018, positioned near the bottom 1042 of theconstant hydrostatic head reservoir 1014, contains a stopcock 1020 forstarting/stopping the delivery of salt solution 1032. The outlet 1044 ofthe delivery tube 1018 is dimensioned to be inserted through the secondlid opening 1136 in the cylinder lid 1116, with its end positioned belowthe surface of the salt solution 1032 in the cylinder 1120 (after the5.00 cm height of the salt solution 1032 is attained in the cylinder1120). The air-intake tube 1010 is held in place with an o-ring collar(not shown). The constant hydrostatic head reservoir 1014 can bepositioned on a laboratory jack 1016 in order to adjust its heightrelative to that of the cylinder 1120. The components of the constanthydrostatic head reservoir 1014 are sized so as to rapidly fill thecylinder 1120 to the required height (i.e., hydrostatic head) andmaintain this height for the duration of the measurement. The constanthydrostatic head reservoir 1014 must be capable of delivering saltsolution 1032 at a flow rate of at least 3 g/sec for at least 10minutes.

The piston/cylinder assembly 1028 is positioned on a 16 mesh rigidstainless steel support screen (not shown) (or equivalent) which issupported on a ring stand 1040 or suitable alternative rigid stand. Thissupport screen (not shown) is sufficiently permeable so as to not impedesalt solution 1032 flow and rigid enough to support the stainless steelmesh cloth (not shown) preventing stretching. The support screen (notshown) should be flat and level to avoid tilting the piston/cylinderassembly 1028 during the test. The salt solution 1032 passing throughthe support screen (not shown) is collected in a receiving vessel 1024,positioned below (but not supporting) the support screen (not shown).The receiving vessel 1024 is positioned on the balance 1026 which isaccurate to at least 0.01 g. The digital output of the balance 1026 isconnected to a computerized data acquisition system (not shown).

Preparation of Reagents (not Illustrated)

Jayco Synthetic Urine (JSU) 1312 (see FIG. 5) is used for a swellingphase (see UPM

Procedure below) and 0.118 M Sodium Chloride (NaCl) Solution is used fora flow phase (see UPM Procedure below). The following preparations arereferred to a standard 1 liter volume.

For preparation of volumes other than 1 liter, all quantities are scaledaccordingly.

JSU: A 1 L volumetric flask is filled with distilled water to 80% of itsvolume, and a magnetic stir bar is placed in the flask. Separately,using a weighing paper or beaker the following amounts of dryingredients are weighed to within ±0.01 g using an analytical balanceand are added quantitatively to the volumetric flask in the same orderas listed below. The solution is stirred on a suitable stir plate untilall the solids are dissolved, the stir bar is removed, and the solutiondiluted to 1 L volume with distilled water. A stir bar is againinserted, and the solution stirred on a stirring plate for a few minutesmore.

Quantities of salts to make 1 liter of Jayco Synthetic Urine:

Potassium Chloride (KCl) 2.00 g

Sodium Sulfate (Na₂SO4) 2.00 g

Ammonium dihydrogen phosphate (NH4H2PO4) 0.85 g

Ammonium phosphate, dibasic ((NH4)2HPO4) 0.15 g

Calcium Chloride (CaCl2) 0.19 g—[or hydrated calcium chloride(CaCl2.2H2O) 0.25 g]

Magnesium chloride (MgCl2) 0.23 g—[or hydrated magnesium chloride(MgCl2.6H2O)0.50 g]

To make the preparation faster, each salt is completely dissolved beforeadding the next one. Jayco synthetic urine may be stored in a cleanglass container for 2 weeks. The solution should not be used if itbecomes cloudy. Shelf life in a clean plastic container is 10 days.0.118 M Sodium Chloride (NaCl) Solution: 0.118 M Sodium Chloride is usedas salt solution 1032. Using a weighing paper or beaker 6.90 g (±0.01 g)of sodium chloride is weighed and quantitatively transferred into a 1 Lvolumetric flask; and the flask is filled to volume with distilledwater. A stir bar is added and the solution is mixed on a stirring plateuntil all the solids are dissolved.

Test Preparation

Using a solid reference cylinder weight (not shown) (40 mm diameter; 140mm height), a caliper gauge (not shown) (e.g., Mitotoyo Digimatic HeightGage) is set to read zero. This operation is conveniently performed on asmooth and level bench top 1046. The piston/cylinder assembly 1028without SAP particles is positioned under the caliper gauge (not shown)and a reading, L1, is recorded to the nearest 0.01 mm.

The constant hydrostatic head reservoir 1014 is filled with saltsolution 1032. The bottom 1034 of the air-intake tube 1010 is positionedso as to maintain the top part (not shown) of the liquid meniscus (notshown) in the cylinder 1120 at the 5.00 cm mark 1156 during themeasurement. Proper height alignment of the air-intake tube 1010 at the5.00 cm mark 1156 on the cylinder 1120 is critical to the analysis.

The receiving vessel 1024 is placed on the balance 1026 and the digitaloutput of the balance 1026 is connected to a computerized dataacquisition system (not shown). The ring stand 1040 with a 16 mesh rigidstainless steel support screen (not shown) is positioned above thereceiving vessel 1024. The 16 mesh screen (not shown) should besufficiently rigid to support the piston/cylinder assembly 1028 duringthe measurement. The support screen (not shown) must be flat and level.

UPM Procedure

1.5 g (±0.05 g) of SAP particles is weighed onto a suitable weighingpaper or weighing aid using an analytical balance. The moisture contentof the SAP particles is measured according to the Edana Moisture ContentTest Method 430.1-99 (“Superabsorbent materials—Polyacrylatesuperabsorbent powders—Moisture Content—weight loss upon heating”(February 99)). If the moisture content of the SAP particles is greaterthan 5%, then the SAP particles weight should be corrected for moisture(i.e., in that particular case the added SAP particles should be 1.5 gon a dry-weight basis).

The empty cylinder 1120 is placed on a level benchtop 1046 and the SAPparticles are quantitatively transferred into the cylinder 1120. The SAPparticles are evenly dispersed on the screen (not shown) attached to thebottom 1148 of the cylinder 1120 by gently shaking, rotating, and/ortapping the cylinder 1120. It is important to have an even distributionof particles on the screen (not shown) attached to the bottom 1148 ofthe cylinder 1120 to obtain the highest precision result. After the SAPparticles have been evenly distributed on the screen (not shown)attached to the bottom 1148 of the cylinder 1120 particles must notadhere to the inner cylinder walls 1150. The piston shaft 1114 isinserted through the first lid opening 1134, with the lip 1154 of thelid 1116 facing towards the piston head 1118. The piston head 1118 iscarefully inserted into the cylinder 1120 to a depth of a fewcentimeters. The lid 1116 is then placed onto the upper rim 1144 of thecylinder 1120 while taking care to keep the piston head 1118 away fromthe SAP particles. The lid 1116 and piston shaft 1126 are then carefullyrotated so as to align the third, fourth, fifth, and sixth linear indexmarks are then aligned. The piston head 1118 (via the piston shaft 1114)is then gently lowered to rest on the dry SAP particles. The weight 1112is positioned on the upper portion 1128 of the piston shaft 1114 so thatit rests on the shoulder 1124 such that the first and second linearindex marks are aligned. Proper seating of the lid 1116 prevents bindingand assures an even distribution of the weight on the hydrogel layer1318.

Swelling Phase: An 8 cm diameter fritted disc (7 mm thick; e.g.Chemglass Inc. #CG 201-51, coarse porosity) 1310 is saturated by addingexcess JSU 1312 to the fritted disc 1310 until the fritted disc 1310 issaturated. The saturated fritted disc 1310 is placed in a wideflat-bottomed Petri dish 1314 and JSU 1312 is added until it reaches thetop surface 1316 of the fritted disc 1310. The JSU height must notexceed the height of the fitted disc 1310.

The screen (not shown) attached to the bottom 1148 of the cylinder 1120is easily stretched. To prevent stretching, a sideways pressure isapplied on the piston shaft 1114, just above the lid 1116, with theindex finger while grasping the cylinder 1120 of the piston/cylinderassembly 1028. This “locks” the piston shaft 1114 in place against thelid 1116 so that the piston/cylinder assembly 1028 can be lifted withoutundue force being exerted on the screen (not shown).

The entire piston/cylinder assembly 1028 is lifted in this fashion andplaced on the fritted disc 1310 in the Petri dish 1314. JSU 1312 fromthe Petri dish 1314 passes through the fritted disc 1310 and is absorbedby the SAP particles (not shown) to form a hydrogel layer 1318. The JSU1312 available in the Petri dish 1314 should be enough for all theswelling phase. If needed, more JSU 1312 may be added to the Petri dish1314 during the hydration period to keep the JSU 1312 level at the topsurface 1316 of the fritted disc 1310. After a period of 60 minutes, thepiston/cylinder assembly 1028 is removed from the fritted disc 1310,taking care to lock the piston shaft 1114 against the lid 1116 asdescribed above and ensure the hydrogel layer 1318 does not lose JSU1312 or take in air during this procedure. The piston/cylinder assembly1028 is placed under the caliper gauge (not shown) and a reading, L2, isrecorded to the nearest 0.01 mm. If the reading changes with time, onlythe initial value is recorded. The thickness of the hydrogel layer 1318,L0 is determined from L2−L1 to the nearest 0.1 mm.

The piston/cylinder assembly 1028 is transferred to the support screen(not shown) attached to the ring support stand 1040 taking care to lockthe piston shaft 1114 in place against the lid 1116. The constanthydrostatic head reservoir 1014 is positioned such that the deliverytube 1018 is placed through the second lid opening 1136. The measurementis initiated in the following sequence:

a) The stopcock 1020 of the constant hydrostatic head reservoir 1014 isopened to permit the salt solution 1032 to reach the 5.00 cm mark 1156on the cylinder 1120. This salt solution 1032 level should be obtainedwithin 10 seconds of opening the stopcock 1020.

b) Once 5.00 cm of salt solution 1032 is attained, the data collectionprogram is initiated.

With the aid of a computer (not shown) attached to the balance 1026, thequantity of salt solution 1032 passing through the hydrogel layer 1318is recorded at intervals of 20 seconds for a time period of 10 minutes.At the end of 10 minutes, the stopcock 1020 on the constant hydrostatichead reservoir 1014 is closed.

The data from 60 seconds to the end of the experiment are used in theUPM calculation. The data collected prior to 60 seconds are not includedin the calculation. The flow rate Fs (in g/s) is the slope of a linearleast-squares fit to a graph of the weight of salt solution 1032collected (in grams) as a function of time (in seconds) from 60 secondsto 600 seconds.

The Urine Permeability Measurement (Q) of the hydrogel layer 1318 iscalculated using the following equation:

Q=[Fg×L0]/[ρ×A×ΔP],

where Fg is the flow rate in g/sec determined from regression analysisof the flow rate results, L0 is the initial thickness of the hydrogellayer 1318 in cm, ρ is the density of the salt solution 1032 in gm/cm3.A (from the equation above) is the area of the hydrogel layer 1318 incm2, ΔP is the hydrostatic pressure in dyne/cm2, and the UrinePermeability Measurement, Q, is in units of cm3 sec/gm. The average ofthree determinations should be reported.

FSR Test method

This method determines the speed of SAP particles, especially polymerichydrogelling particles, such as cross-linked poly-acrylates to swell in0.9% Saline (aqueous 0.9 mass % NaCl solution). The measurementprinciple is to allow SAP particles to absorb a known amount of fluid,and the time taken to absorb the fluid is measured. The result is thenexpressed in grams of absorbed fluid per gram of material per second.All testing is conducted at 23±2° C.

Four grams of a representative sample of the SAP particles is dried inan uncovered 5 cm diameter Petri dish in a vacuum chamber at 23±2° C.and 0.01 torr or lower for 48 hours prior to measurement.

About 1 g (+/−0.1 g) of the test specimen is removed from the vacuumchamber and immediately weighed to an accuracy of 0.001 g into a 25 mlbeaker, which has 32 to 34 mm inside diameter, and 50 mm height. Thematerial is evenly spread over the bottom. 20 g of 0.9% Saline areweighed to an accuracy of +/−0.01 g in a 50 ml beaker, and are thenpoured carefully but quickly into the beaker containing the testmaterial. A timer is started immediately upon the liquid contacting thematerial. The beaker is not moved or agitated during swelling.

The timer is stopped, and the time recorded to the nearest second (ormore accurately if appropriate), when the last part of undisturbed fluidis reached by the swelling particles. In order to increase thereproducibility of the determination of the end point, the liquidsurface can be illuminated by a small lamp without heating the surfaceby that lamp. The beaker is re-weighed to determine the actually pickedup liquid to within ±0.1 g.

The free-swell rate is calculated by dividing the weight of SAPparticles by the amount of actually picked up liquid, and dividing theresult by the time required for this pick up, and is expressed in“g/g/s”. Three measurements are performed and the results averaged toobtain the FSR value in g/g/s, reported to 3 significant figures.

EXAMPLES

For Examples 1 and 2 the supercritical fluid extraction unit asdescribed in Zetzl et al. (2003), “Standardised Low Cost SFE—Units forUniversity Education and Comparative Research”, Proceedings of the 6thInternational Symposium on Supercritical Fluides, Versailles, (2),577-581, ISBN 2-905-267-37-02 has been used. For Examples 3 and 4 theequipment used was generally similar, but the extractor had a volume of1000 ml. Also, the equipment differed from the one of Examples 1 and 2in that it was a “closed loop” system to allow the solvent (e.g. CO₂) tobe recycled. The 1000 unit allows for a significantly higher mass flow:While the 100 ml unit of Examples 1 and 2 enables up to 2 kg/hoursolvent flow, the 1000 ml unit allows up to 10 kg/hour of solvent flow.Also, the 1000 ml unit allows pressure up to 1000 bar and temperaturesup to 100° C.

Example 1

The SAP particles of Example 1 are the superabsorbent polymer particleswhich are used in Pampers “Cruisers” diapers commercially available inthe USA in February 2011. These SAP particles are generally madeaccording to US 2009/0275470A1. Two samples (Sample 1 and 2) were testedunder the same conditions.

Amount of SAP particles: 8 g

Solvent: CO2

Autoclave pressure: 450 bar

Autoclave temperature: 45° C.

Flow rate: 0.7 kg/h

Extraction time: 120 min

CRC, FSR and UPM were measured before and after the samples weresubjected to the supercritical fluid treatment.

Results

UPM CRC FSR (1 × 10⁻⁷ (g/g) (g/g/s) (cm³ · s)/g) Sample 1 before SCFtreatment 26.8 0.25 102 Sample 1 after SCF treatment 26.9 0.23 101Sample 2 before SCF treatment 26.3 0.15 94 Sample 2 after SCF treatment26.2 0.14 103

The data show that the capacity (CRC), free swell rate (FSR) and thepermeability (UPM) of SAP particles do not decrease during the SCFtreatment, at least as long as pure SAP particles samples are tested,i.e. as long as the SAP particles are not contaminated and are notcomprised in an absorbent article.

Examples 2 to 4 focus on the behavior of contaminated SAP particleswithin an absorbent article when subjected to SCF treatment.

Example 2

Pampers “Cruisers” diapers, Size 5, as marketed in the USA in February2011 (Samples 3 to 6) have been subjected different extractionconditions. The absorbent cores of these diapers comprise 12.8 g of SAPparticles and 0.84 g of solidified thermoplastic composition. The SAPparticles are immobilized by the solidified thermoplastic composition.It should be noted however, that the complete diaper comprises 1.83 g ofsolidified thermoplastic composition, as various components within thearticle are adhered to each other using such a solidified thermoplasticcomposition (e.g. when gluing the topsheet to the backsheet at theperiphery or when attaching leg elastics to nonwoven layers surroundingthem). During extraction, all thermoplastic compositions within thearticle are affected by the supercritical fluid. As all the solidifiedthermoplastic compositions are extracted, the absorbent article willfall apart into separate pieces relatively easily after the SCFtreatment.

Sample 3 (1 Diaper)

Solvent: CO₂

Autoclave pressure: 450 bar

Autoclave temperature: 45° C.

Flow rate: 0.5 kg/h

Extraction time: 90 min

Sample 4 (1 Diaper)

Solvent: CO₂

Autoclave pressure: 500 bar

Autoclave temperature: 45° C.

Flow rate: 0.8 kg/h

Extraction time: 115 min

Sample 5 (1 Diaper)

Solvent: CO₂ and Ethanol

Autoclave pressure: 350 bar

Autoclave temperature: 45° C.

Flow rate: 0.5 kg/h CO₂ and 6 ml/h Ethanol

Extraction time: 120 min

Sample 6 (1 Diaper)

Solvent: CO₂

Autoclave pressure: 350 bar

Autoclave temperature: 45° C.

Flow rate: 0.7 kg/h CO₂

Extraction time: 120 min

After extraction treatment in the SCF unit, the SAP particles wereseparated from the solidified thermoplastic compositions, with whichthey were contaminated in the diaper prior to extraction. The recycledparticles were then tested for their CRC and UPM values. The respectivevalues of the raw material SAP particles, which were used to manufacturethe diapers of Samples 3 to 6 were also measured. For the CRCmeasurements, the moisture content of the SAP particles recycled fromSamples 3 to 6 was the same as the moisture content of the raw materialSAP particles.

Results

UPM CRC (1 × 10⁻⁷ (g/g) (cm³ · s)/g) Sample 3 26.9 63 Sample 4 26.2 63Sample 5 26.7 60 Sample 6 26.5 62 Raw material SAP particles 26.8 93

The data show that the capacity (CRC) of the SAP particles does notdecrease due to the SCF treatment, however, the permeability values(UPM) decrease. The UPM value does not decrease to an extent that therecycled SAP particles cannot be used in absorbent articles, especiallyif they are mixed with non-recycled SAP particles. The overall qualityof the SAP particles was good for all four different extractionconditions.

Example 3

Pampers “Cruisers” diapers, Size 5, as marketed in the USA in February2011 (Sample 7) have been subjected to SCF treatment in a unit having a1000 ml extractor:

Sample 7 (5 Diapers in the 1000 ml Extractor)

Solvent: CO₂

Autoclave pressure: 375 bar

Autoclave temperature: 45° C.

Flow rate: 2.2 kg/h

Extraction time: 180 min

Recycling of Carbon dioxide at 55 bar, 17° C.

After extraction treatment in the SCF unit, the SAP particles wereseparated from the solidified thermoplastic compositions, with whichthey were contaminated in the diaper prior to extraction. The recycledparticles were then tested for their CRC, FSR and UPM values. Therespective values of the raw material SAP particles, which were used tomanufacture the diapers of Sample 7 were also measured. For the CRCmeasurement, the moisture content of the SAP particles recycled fromSample 7 was the same as the moisture content of the raw material SAPparticles.

Results

UPM CRC FSR (1 × 10⁻⁷ (g/g) (g/g/s) (cm³ · s)/g) Sample 7 27.4 0.27 59Raw material SAP particles 26.8 0.27 90

The data show that the capacity (CRC) and the FSR of the SAP particlesdoes not decrease due to the SCF treatment, however, the permeabilityvalues (UPM) decrease. As for the samples of Example 2, the UPM value ofsample 7 does not decrease to an extent that the recycled SAP particlescannot be used in absorbent articles, especially if they are mixed withnon-recycled SAP particles. The overall quality of the SAP particles wasgood.

Example 4

Pampers “Cruisers” diapers, Size 5, as marketed in the USA in February2011 (Sample 7) have been subjected to SCF treatment in a unit having a1000 ml extractor and using different extraction conditions:

Sample 8 (5 Diapers in the 1000 ml Extractor)

Solvent: CO₂

Autoclave pressure: 300 bar

Autoclave temperature: 45° C.

Flow rate: 2.2 kg/h

Extraction time: 180 min

Recycling of Carbon dioxide at 55 bar, 17° C.

Sample 9 (5 Diapers in the 1000 ml Extractor)

Solvent: CO₂

Autoclave pressure: 300 bar

Autoclave temperature: 45° C.

Flow rate: 7.8 kg/h

Extraction time: 60 min

Recycling of Carbon dioxide at 55 bar, 17° C.

Sample 10 (5 Diapers in the 1000 ml Extractor)

Solvent: CO₂

Autoclave pressure: 350 bar

Autoclave temperature: 45° C.

Flow rate: 7.5 kg/h

Extraction time: 60 min

Recycling of Carbon dioxide at 55 bar, 17° C.

After extraction treatment in the SCF unit, the SAP particles wereseparated from the solidified thermoplastic compositions, with whichthey were contaminated in the diaper prior to extraction. The recycledparticles were then tested for their CRC, FSR and UPM values. Therespective values of the raw material SAP particles, which were used tomanufacture the diapers of Samples 8, 9 and 10 were also measured. Forthe CRC, measurement, the moisture content of the SAP particles recycledfrom Samples 8, 9 and 10 was the same as the moisture content of the rawmaterial SAP particles.

Results

UPM CRC FSR (1 × 10⁻⁷ (g/g) (g/g/s) (cm³ · s)/g) Sample 8 27.3 0.23 64Sample 9 27.2 0.21 59 Sample 10 27.1 0.26 63 Raw material SAP particles26.8 0.30 93

The data show that the capacity (CRC) and the FSR of the SAP particlesdoes not decrease due to the SCF treatment, however, the permeabilityvalues (UPM) decrease. As for the samples of Examples 2 and 3, the UPMvalue of samples 8, 9 and 10 does not decrease to an extent that therecycled SAP particles cannot be used in absorbent articles, especiallyif they are mixed with non-recycled SAP particles. The overall qualityof the SAP particles was good.

All patents and patent applications (including any patents which issuethereon) assigned to the Procter & Gamble Company referred to herein arehereby incorporated by reference to the extent that it is consistentherewith.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. An absorbent core comprising superabsorbent polymer particles,wherein a part of the superabsorbent polymer particles are recycledsuperabsorbent polymer particles, the recycling comprising separatingcontaminated superabsorbent polymer particles from a solidifiedthermoplastic composition.
 2. An absorbent core according to claim 1,wherein the contaminated superabsorbent polymer particles have a ratioof superabsorbent polymer particles to solidified thermoplasticcomposition of from about 10 to about
 1. 3. An absorbent core accordingto claim 2, wherein the ratio is from about 10 to about 0.5.
 4. Anabsorbent core according to claim 1, wherein the contaminatedsuperabsorbent polymer particles are separated from the solidifiedthermoplastic composition using a supercritical fluid comprising carbondioxide, propane, or mixtures thereof.
 5. An absorbent core according toclaim 1, wherein the recycled superabsorbent polymer particles are morethan about 1 weight percent of the total amount of superabsorbentpolymer particles comprised by the absorbent core.
 6. An absorbent coreaccording to claim 5, wherein the recycled superabsorbent polymerparticles are more than about 5 weight percent of the total amount ofsuperabsorbent polymer particles comprised by the absorbent core.
 7. Anabsorbent core according to claim 1, wherein the recycled superabsorbentpolymer particles are less than about 70 weight percent of the totalamount of superabsorbent polymer particles comprised by the absorbentcore.
 8. An absorbent core according to claim 7, wherein the recycledsuperabsorbent polymer particles are less than about 50 weight percentof the total amount of superabsorbent polymer particles comprised by theabsorbent core.
 9. An absorbent core according to claim 8, wherein therecycled superabsorbent polymer particles are less than about 20 weightpercent of the total amount of superabsorbent polymer particlescomprised by the absorbent core.
 10. An absorbent core according toclaim 9, wherein the recycled superabsorbent polymer particles are lessthan about 15 weight percent of the total amount of superabsorbentpolymer particles comprised by the absorbent core.
 11. An absorbent coreaccording to claim 1, wherein the absorbent core comprises a blend ofthe recycled superabsorbent polymer particles and non-recycledsuperabsorbent polymer particles, and wherein the recycledsuperabsorbent polymer particles and the non-recycled superabsorbentpolymer particles have been mixed with each other prior to incorporatingthem in the absorbent core.
 12. An absorbent core according to claim 1,wherein the Urine Permeability Measurement (UPM) value of the recycledsuperabsorbent polymer particles does not decrease by more than about40% during the process of recycling.
 13. An absorbent core according toclaim 12, wherein the UPM value of the recycled superabsorbent polymerparticles does not decrease by more than about 35% during the process ofrecycling.
 14. An absorbent core according to claim 13, wherein the UPMvalue of the recycled superabsorbent polymer particles does not decreaseby more than about 30% during the process of recycling.
 15. An absorbentcore according to claim 1, wherein the recycled superabsorbent particleshave an UPM value of from about 60% to about 95% compared to the UPMvalue of the non-recycled superabsorbent polymer particles.
 16. Anabsorbent core according to claim 1, wherein the recycled superabsorbentpolymer particles have an UPM value of at least about 50 (10⁻⁷(cm³·s)/g), and wherein the non-recycled superabsorbent polymerparticles have an UPM value of at least about 80 (10⁻⁷ (cm³·s)/g). 17.An absorbent core according to claim 16, wherein the recycledsuperabsorbent polymer particles have an UPM value of at least about 60(10⁻⁷ (cm³·s)/g).
 18. An absorbent core according to claim 16, whereinthe non-recycled superabsorbent polymer particles have an UPM value ofat least about 100 (10⁻⁷ (cm³·s)/g).
 19. An absorbent core according toclaim 1, wherein separating contaminated superabsorbent polymerparticles from a solidified thermoplastic composition comprises thesteps of: a) providing agglomerates of contaminated superabsorbentpolymer particles and the solidified thermoplastic composition, whereinat least a part of the contaminated superabsorbent polymer particles areadhered to at least a part of the solidified thermoplastic composition;b) subjecting the agglomerates to a supercritical fluid comprisingcarbon dioxide, propane, or mixtures thereof.
 20. An absorbent coreaccording to claim 1, wherein the solidified thermoplastic compositioncomprises at least 30 weight percent of a thermoplastic polymer based onthe weight of the solidified thermoplastic composition.
 21. An absorbentcore according to claim 1, wherein the absorbent core is comprisedwithin an absorbent article, the absorbent article being selected fromthe group consisting of diapers, training pants, and sanitary napkins.22. A method of providing superabsorbent polymer particles in absorbentcores, wherein at least a part of the superabsorbent polymer particlesare recycled superabsorbent polymer particles, the recycling comprisesseparating contaminated superabsorbent polymer particles from asolidified thermoplastic composition.
 23. A method of providingsuperabsorbent polymer particles according to claim 22, wherein therecycled superabsorbent polymer particles are more than about 5 weightpercent of the total amount of superabsorbent polymer particles in theabsorbent core and wherein the recycled superabsorbent polymer particlesare less than about 15 weight percent of the total amount ofsuperabsorbent polymer particles comprised by the absorbent core.
 24. Amethod for separating superabsorbent polymer particles from a solidifiedthermoplastic composition, the method comprising the steps of: a)providing agglomerates of the superabsorbent polymer particles and thesolidified thermoplastic composition, wherein at least a part of thesuperabsorbent polymer particles are adhered to at least a part of thesolidified thermoplastic composition, b) subjecting the agglomerates toa supercritical fluid comprising carbon dioxide, propane, or mixturesthereof, wherein the UPM value of the separated superabsorbent polymerparticles does not decrease by more than about 40% while thesuperabsorbent polymer particles are subjected to steps a) and b).
 25. Amethod according to claim 24, wherein for step a), the ratio ofsuperabsorbent polymer particles to solidified thermoplastic compositionis from about 10 to about 0.5.
 26. A method according to claim 24,wherein the supercritical fluid further comprises from about 0.1 toabout 20 weight percent, based on the total weight of supercriticalfluid, of one or more co-solvents, the co-solvents being selected fromthe group consisting of ethanol, ethyl acetate, butane, butyl acetate,acetone, nitrous oxide, carbon dioxide, nitrogen, water, and mixturesthereof.
 27. A method of providing superabsorbent polymer particles inan absorbent core, wherein at least a part of the superabsorbent polymerparticles are recycled superabsorbent polymer particles, the recycledsuperabsorbent polymer particles being obtained according to the methodof claim 24.